slotted GTS rotors?
05-28-2009, 03:04 PM
#16
Rennlist Member
Or did I sell you 964 rotors too. I am getting old. 
05-28-2009, 04:21 PM
#18
Nordschleife Master
Edit:
looking at the picture of the cracked rotor, is that a 928? If so is this the leading or trailing side of the rotor. I am just speculating but it looks like I see drop links which would make it the trailing and that would mean these rotors are installed facing the wrong way. The cooling veins would be going in the wrong direction for proper cooling. I would be curious to know if that is the case.
05-28-2009, 06:19 PM
#19
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05-28-2009, 06:20 PM
#20
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05-28-2009, 06:29 PM
#21
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Thread Starter
What kind of racer do you think I am to put on a rotor backward!!????? 
Anyway, I wish that was the problem, but its not. that is the leading edge on the driver side of the car.
Racing does some pretty strange stuff to equipment, that backing off just a second or two a lap would never do. These rotors are glowing in some sections of the track. the cracking is fairly normal, after near a full season, and I would pitch the rotors when the cracks propagated to the outside diameter. I thought with the greater mass of the larger rotors, that this problem might be mitigated. Looks like the slightly better clamping force and greater speeds of the stroker, have cooked these rotors as well. Im cooking the pads, but they are holding up better than the pagid oranges (Blacks). Just too much heat!
I did feel some vibration the pedal that could have been some warping that could have provided a highside that caused the cracking. the other side looks fine and the other parts of the cracked rotor looks fine as well. I never had any issues with the zimmerman rotors , so I wonder if the different casting was an issue.
As far as cooling, i always do a cool down lap with no brakes , and still the temps in the paddock are near 400 degrees front and 300 degrees rear.
I usually cool them down for 2 laps in practice and qual, never coming to a stop unless they have been cooled.
mk
Anyway, I wish that was the problem, but its not. that is the leading edge on the driver side of the car.
Racing does some pretty strange stuff to equipment, that backing off just a second or two a lap would never do. These rotors are glowing in some sections of the track. the cracking is fairly normal, after near a full season, and I would pitch the rotors when the cracks propagated to the outside diameter. I thought with the greater mass of the larger rotors, that this problem might be mitigated. Looks like the slightly better clamping force and greater speeds of the stroker, have cooked these rotors as well. Im cooking the pads, but they are holding up better than the pagid oranges (Blacks). Just too much heat!
I did feel some vibration the pedal that could have been some warping that could have provided a highside that caused the cracking. the other side looks fine and the other parts of the cracked rotor looks fine as well. I never had any issues with the zimmerman rotors , so I wonder if the different casting was an issue.
As far as cooling, i always do a cool down lap with no brakes , and still the temps in the paddock are near 400 degrees front and 300 degrees rear.
I usually cool them down for 2 laps in practice and qual, never coming to a stop unless they have been cooled.
mk
Wow I do tech for many events and that is the worst case of cracking I have ever seen. Usually you warp your rotors long before that occurs.
What do you need to do to crack a rotor like that? My C2 has big reds with 965 rotors and the car is a dual driver car. I actually out brake the ABS and tires and heat them up quite good with my wife driving after me. Wonder if her driving at a slower rate and far easier braking has helped prolong my rotors. But these are mine after 7k track miles using pagid yellows. They are at their wear limits and need to be replaced.
Is it possible that all the cracking comes from cooling down the brakes properly after a hard run?
Edit:
looking at the picture of the cracked rotor, is that a 928? If so is this the leading or trailing side of the rotor. I am just speculating but it looks like I see drop links which would make it the trailing and that would mean these rotors are installed facing the wrong way. The cooling veins would be going in the wrong direction for proper cooling. I would be curious to know if that is the case.
What do you need to do to crack a rotor like that? My C2 has big reds with 965 rotors and the car is a dual driver car. I actually out brake the ABS and tires and heat them up quite good with my wife driving after me. Wonder if her driving at a slower rate and far easier braking has helped prolong my rotors. But these are mine after 7k track miles using pagid yellows. They are at their wear limits and need to be replaced.
Is it possible that all the cracking comes from cooling down the brakes properly after a hard run?
Edit:
looking at the picture of the cracked rotor, is that a 928? If so is this the leading or trailing side of the rotor. I am just speculating but it looks like I see drop links which would make it the trailing and that would mean these rotors are installed facing the wrong way. The cooling veins would be going in the wrong direction for proper cooling. I would be curious to know if that is the case.
05-28-2009, 06:32 PM
#22
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Thread Starter
no BINGO! they are on correctly. That picture was the driver side. It spins counterclockwise. that metalic thing you see, i think is a sliver of light shinnig through the wheel. If it was trailing edge, there would be a big fat S4 caliper there ! 
mk
mk
Last edited by mark kibort; 05-28-2009 at 06:47 PM.
05-28-2009, 06:40 PM
#23
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Some brake-cooling ducts would help. A lot...in fact, a duct with an E-Ram blower on each side would be good.. My Nascar pal showed me a set of three blowers they use on each side of the front, for road racing...
05-28-2009, 06:45 PM
#24
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We had a deal going with a nascar team to use the eRAM for brake cooling and downforce. a company I delt with in the factory automation space, was using the same fan as we used for a nascar brake cooling design.
Here is the same rotor w but on the other side. notice the cracks are very faint, about par for 4 races even with the smaller diameter rotors.
Here is the same rotor w but on the other side. notice the cracks are very faint, about par for 4 races even with the smaller diameter rotors.
05-28-2009, 08:21 PM
#26
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Will do. Ill have to rig up some cooling hoses. Wonder how bad no slots will work? heck, others are out there without slots. the Comp couple has 14" rotors with no slots (not the WCGT version of the Viper Compcoupe)
mk
mk
05-28-2009, 10:12 PM
#27
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I have a full set of solid GTS rotors that just came off my '93 GTS if anybody wants them. Just pay shipping. They are fine, just need to be turned and repainted.
05-28-2009, 11:14 PM
#28
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05-29-2009, 11:13 AM
#29
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This is pretty common and what I normally see. I wasn't sure if that was your car because you mentioned a 964. You are lucky they didn't explode and lock up on you.
I have seen some racers use the GTS rotors and they cracked also but took longer. They usually start at the edge which is a problem.
I would think going with the big red 58 mm pad might help dissipate the heat better. i am assuming your biasing has the rears doing equal work and that this is not a case of the fronts working overtime. Just throwing thoughts out.
I have had my brakes glow red too and still no cracks. People tell me I am not braking hard enough if I am not seeing more cracking and are surprised my rotors look so good and evenly worn. Yet I am exceeding the lockup point of the ABS and sometimes the tire grip with R compounds. I am starting to think that cooling down the brakes might have more of an impact than we think. 400 degrees is still quite hot and is probably hotter than when my wife comes in after her runs. When we switch drivers (I almost always end up being her tire warmer) You can smell the brakes and hear them contracting. When she comes in I don't smell anything and no sounds at all. i will measure the temps after she comes in and see what they are at. This might have more to do with cracking than we think and possibly a drive around the paddock a few times might help with longevity.
I have seen some racers use the GTS rotors and they cracked also but took longer. They usually start at the edge which is a problem.
I would think going with the big red 58 mm pad might help dissipate the heat better. i am assuming your biasing has the rears doing equal work and that this is not a case of the fronts working overtime. Just throwing thoughts out.
I have had my brakes glow red too and still no cracks. People tell me I am not braking hard enough if I am not seeing more cracking and are surprised my rotors look so good and evenly worn. Yet I am exceeding the lockup point of the ABS and sometimes the tire grip with R compounds. I am starting to think that cooling down the brakes might have more of an impact than we think. 400 degrees is still quite hot and is probably hotter than when my wife comes in after her runs. When we switch drivers (I almost always end up being her tire warmer) You can smell the brakes and hear them contracting. When she comes in I don't smell anything and no sounds at all. i will measure the temps after she comes in and see what they are at. This might have more to do with cracking than we think and possibly a drive around the paddock a few times might help with longevity.
05-29-2009, 12:35 PM
#30
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Thread Starter
This cracking shown here is normal for holed rotors. remember, ive been abusing the S4 size rotors for YEARS now (7 full racing seasons) they crack-out at about mid season. these started show cracking at an earlier time, as my thoughts were maybe that the porsche rotors were not the quality as the zimmermans. anyway, the extra force with the diameter, with the more aggresive pad has caused this issue. a wider pad wouldnt do much as most racing systems have this size of pad. Stoptech uses the S4 pad on their 13" brake system. (so does ferrari use near the same size pad on their 14" system) I did feel a vibration at sears that went away at laguna, but that could have been a warping that started a hot spot and then the cracking area at one specific area. dont know. Ill try the GTS rotors and see if steve can put some slots on them.
Here is the pic of my old S4 rotors after almost an entire racing season.
mk
Here is the pic of my old S4 rotors after almost an entire racing season.
mk
This is pretty common and what I normally see. I wasn't sure if that was your car because you mentioned a 964. You are lucky they didn't explode and lock up on you.
I have seen some racers use the GTS rotors and they cracked also but took longer. They usually start at the edge which is a problem.
I would think going with the big red 58 mm pad might help dissipate the heat better. i am assuming your biasing has the rears doing equal work and that this is not a case of the fronts working overtime. Just throwing thoughts out.
I have had my brakes glow red too and still no cracks. People tell me I am not braking hard enough if I am not seeing more cracking and are surprised my rotors look so good and evenly worn. Yet I am exceeding the lockup point of the ABS and sometimes the tire grip with R compounds. I am starting to think that cooling down the brakes might have more of an impact than we think. 400 degrees is still quite hot and is probably hotter than when my wife comes in after her runs. When we switch drivers (I almost always end up being her tire warmer) You can smell the brakes and hear them contracting. When she comes in I don't smell anything and no sounds at all. i will measure the temps after she comes in and see what they are at. This might have more to do with cracking than we think and possibly a drive around the paddock a few times might help with longevity.
I have seen some racers use the GTS rotors and they cracked also but took longer. They usually start at the edge which is a problem.
I would think going with the big red 58 mm pad might help dissipate the heat better. i am assuming your biasing has the rears doing equal work and that this is not a case of the fronts working overtime. Just throwing thoughts out.
I have had my brakes glow red too and still no cracks. People tell me I am not braking hard enough if I am not seeing more cracking and are surprised my rotors look so good and evenly worn. Yet I am exceeding the lockup point of the ABS and sometimes the tire grip with R compounds. I am starting to think that cooling down the brakes might have more of an impact than we think. 400 degrees is still quite hot and is probably hotter than when my wife comes in after her runs. When we switch drivers (I almost always end up being her tire warmer) You can smell the brakes and hear them contracting. When she comes in I don't smell anything and no sounds at all. i will measure the temps after she comes in and see what they are at. This might have more to do with cracking than we think and possibly a drive around the paddock a few times might help with longevity.
Last edited by mark kibort; 05-29-2009 at 12:57 PM.